It is known that a large number of different shades are used in industrial painting installations, for example, in painting installations for car bodies or attachments. Painting installations of this type are generally robot-based and, with typical cycle times from 60 s to 90 s, are designed to paint a different shade in each basic cycle, wherein 20 to 60 different shades is a customary number in the automotive industry. Color changers are generally provided in order to supply a paint material of the desired shade to a respective atomizer attached to a robot arm, for example. These color changers have a multiplicity of inputs for paint material, which are connected to corresponding supply lines for the different paint materials. The paint materials are generally provided by means of what are known as ring lines at various delivery points along the painting installation, and from there are guided to the respective color changer by means of the supply lines. A color changer may additionally have a common collecting duct, into which the supply lines discharge at least indirectly, wherein the output of the supply lines is connected via a line to the atomizer to be supplied with paint material.
Valve means are provided between the respective inputs of the color changer and the common collecting duct. Depending on which of the valve means is open, the corresponding paint material is introduced into the collecting duct during painting operation and from there is forwarded to the atomizer. At least one input of a color changer is normally connected via a valve means to a solvent line in order to clean the collecting duct, in the event of a color change, for the next paint material having a different shade. A feed of an air/solvent mixture is often used during a cleaning process and is produced by an alternating, pulsed feed of air and solvent. The cleaning effect of such a mixture is considerably increased with reduced solvent consumption.
The strict separation of different shades is of utmost importance, because even minimal color residues can lead to a distortion of the shade, for example, in the case of a marginal residue of a red shade in a white shade. Valve means are subject to wear and leaks can therefore also occur over time. If a valve means no longer closes reliably, marginal amounts of a paint material of a first shade can infiltrate the collecting duct and mix with a differently colored paint material located therein in spite of an actually closed state of a valve means.
A number of shades can, however, also be mixed due to the accidental simultaneous actuation of a number of valve means, and therefore the painted result is unusable. Even if measures are taken to prevent this by means of a control system, there is still always a residual risk of simultaneous actuation.
The damage caused by erroneously painted vehicle bodies is considerable, because the vehicle body has to be completely reworked and newly painted. Since, in a painting production line, a multiplicity of painting robots is generally involved sequentially in the painting of a single object, an assignment of erroneous painting to a specific painting robot or to the color changer associated therewith has generally proven to be very difficult and sometimes impossible. A painting installation containing a faulty paint changer is therefore generally to be decommissioned for the duration of a fault localization process, whereby the production capacity of the painting installation is reduced disadvantageously.